$ { {-5} \times \left[\begin{array}{rrr}{1} & {-1} & {-2} \\ {2} & {3} & {1}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-5}\times{1} & {-5}\times{-1} & {-5}\times{-2} \\ {-5}\times{2} & {-5}\times{3} & {-5}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-5} & {5} & {10} \\ {-10} & {-15} & {-5}\end{array}\right]}$